New C# 2.0 fact of the day...
I started using Nullable<T> types today for the first time. I found a great use for them - a better default state for API properties. For example, instead of using -1 for the default value for integers, i now use Nullable<int> and set the default to null. Makes it easier to differentiate between null as "initialized" and null as what the caller actually set.
Another key point - i found the Nullable class, and there are some very useful helper methods in there. I needed to use Nullable.Unwrap(o) to grab the inner value from the nullable object. I had a case where i was using reflection to lookup property values, and they were nullable types. So, i had to use the Nullable.Unwrap method to pull out the actual value before using it. If the value was null, then i would skip it.
Cool, eh?